Difference Between Gram Positive and Gram Negative Bacteria

Gram staining is a very important lab test. It paves way to the differentiation of the two distinct bacterial species. It is a faster approach compared to bacterial culture and is very important in identifying the initial working diagnosis of certain disease conditions. So how are the gram negative and positive bacteria different?
Foremost, gram positive bacteria, in a gram staining reaction, will react in a crystal violet dye and will stain dark purple or violet. Its cell wall is unique because it is composed of several peptidoglycan layers (multilayered) making it thicker. This type of bacteria also has the presence of techoic acids, although it lacks an LPS (lipopolysachharide) content, periplasmic space and outer membrane making this group low in both lipoprotein and lipid composition. With regard to its flagellar structure, these bacteria appear to have two rings in their basal bodies. They also produce a different type of toxin from their counterpart as they release exotoxins. They generally have high resistance to physical disruption, dye inhibition, anionic detergent susceptibility, sodium azide and drying resistances.
The gram negative bacteria are different in many ways. This group shows a different gram staining reaction as it normally does not react to a crystal violet dye. However, it usually stains pinkish red and can be decolorized in accepting safranin (a counterstain). It has a thinner peptidoglycan cell wall layer because it is just made of one single layer as opposed to gram positive’s multi-layered wall. Despite its lack of teichoic acids, it makes up for the loss in having a high content of LPS, and has both a periplasmic space and an outer membrane. Due to the latter, it is not surprising that this bacterial group has a high amount of lipoprotein content as well as lipids. In addition, gram negative bacteria have 4 basal body rings and release endotoxins instead of exotoxins. The rest of their characteristics are marked by a general low profile for their dye inhibition, anionic susceptibility, physical disruption, sodium azide and drying resistances.
Because of these differences, the two bacterial groups react differently to certain antibiotics. That’s why doctors first need to know the type of bacteria they are dealing with so that they can prescribe the right type of medications for their patients. Gram negative bacteria cannot be suppressed with penicillin unlike the gram positives because they are basically resistant to this type of antibiotic.

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Written by : Julita.
and updated on December 17, 2010

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